1. Field of the Invention
The present invention relates generally to the production of autostereoscopic pictures of the type employing lenticular screens. More specifically, it concerns novel methods and apparatus for taking and composing such pictures which greatly simplify these processes relative to the prior state of the art.
2. The Prior Art
Lenticular screen-type autostereoscopic pictures are produced basically in two ways, the direct or "in camera" technique, in which the taking and composing steps are both carried out within the camera, and the indirect technique, in which a number of two-dimensional views of an object field are made from different vantage points and the three-dimensional picture is subsequently composed by projecting the two-dimensional images through a composing lenticular screen. As practiced in the prior art, however, both techniques have been subject to use, quality and/or cost limitations which have all but precluded their widespread commercial application.
For example, the direct technique typically requires a specially constructed camera, embodying a lenticular screen sheet located on the emulsion side of the photographic film, and an associated tracking mechanism which constrains movement of the camera to an arcuate path centered around a point in the scene to be photographed. During exposure, the camera is moved along the arcuate path defined by the tracking mechanism and the lenticular screen is shifted relative to the photograhic film by a total distance equal to one lenticule width. This requires precision movements of the various camera and tracking components, with attendant complexity of operation and construction. The apparatus moreover is quite bulky, which limits its usefulness for location photography. The direct process also necessitates exposure times of comparatively long duration, a rather severe limitation, and has the further disadvantage of lacking good depth of field. An additional drawback is that the final three-dimensional picture cannot be freely enlarged or reduced in size.
The indirect technique, by allowing the use of a conventional two-dimensional camera in photographing the object field or scene, eliminates most of the aforementioned drawbacks of the direct technique. Furthermore, recent developments by Lo and Nims relating to the manner of making the two-dimensional exposures, as described in copending, commonly-owned U.S. application Ser. No. 508,810 for "Methods and Apparatus for Taking the Composing Stereoscopic Pictures", filed Sept. 24, 1974, have significantly advanced the state of the art of the indirect technique. Limitations in the composing step have nevertheless continued to impede general usage of the indirect process. This has been due chiefly to the need to produce the final image-bearing sheet (composed of interdigitated lineiform images from the several two-dimensional views) separately from the viewing screen and thereafter to laminate it to the screen with the lineiform images and screen lenticules in precise alignment. Since the image-bearing sheets frequently change size between composing and laminating, as a result for example of fluctuations in ambient temperature, humidity, etc., such alignment of the image sheet and the viewing screen is quite laborious and costly and often cannot be satisfactorily attained. Efforts to apply mass production techniques to the alignment step, by means of litho or offset printing of the image sheet and forming the lenticular screen directly on the image sheet for instance, not only do not adequately eliminate alignment problems but create still other difficulties, such as poor color reproduction, further change of dimension of the image sheet, low density of printing inks, low resolution of the printed image and the like, which further impair the picture quality.
Attempts have been made to overcome the laminating and alignment problems of the indirect composing step by coating a photographic emulsion directly on the rear surface of a lenticular screen and using the "lenticular film" thus produced in composing the final three-dimensional picture from the projected two-dimensional images; that is to say, the lenticular film is used in place of the separate composing lenticular screen and photosensitive sheet. The two-dimensional views are projected sequentially or simultaneously through the lenticular screen to expose the photosensitive emulsion beneath the lenticules. A rudimentary composing system of this nature is described by N. A. Valyus at pages 203-205 of "Stereoscopy", the Focal Press, London W.1, England (1966); see also U.S. Pat. No. 3,482,913, granted Dec. 9, 1969, to W. E. Glenn, Jr. Although avoiding laminating and alignment problems, the prior art indirect composing procedures employing lenticular print film have failed to overcome other problem areas in the composing step. For example, autostereoscopic pictures thus produced have heretofore had limited viewing angles and distances owing to the necessity of viewing the lenticular screen from the same distance and position that the two-dimensional frames were projected during composing. This seriously detracts from the quality of the final picture. It is necessary with known print film composing systems and processes, moreover, to make individual adjustments of the composing system components, such as the distance between enlarging lenses, the projection distance, etc., in order to obtain acceptable sharpness in the three-dimensional picture. Often this is not properly done, with resultant loss of picture quality, and in any event is a costly, time consuming operation. Such adjustments are required, for instance, every time the distance between the camera and the center of interest of the object field, i.e., the element or point to appear in the plane of the three-dimensional picture, is changed. As is developed in detail hereinafter, this necessity compels a substantial number of interrelated adjustments. Heretofore the prior art has neither comprehended the full nature of these adjustments nor provided an effective way of avoiding them or of implementing them in a simplified and reliable manner. The end result has been that the prior art has failed to provide indirect composing apparatus and procedures which are capable of producing high quality autostereoscopic pictures with efficiency and cost factors permissive of widespread commercial application of the technique.
The foregoing and other requirements of the prior art are fulfilled by the present invention.